In a conventional ammonia synthesis process, for example, by using a natural gas, ammonia (NH3) is synthesized from hydrogen (H2) and nitrogen (N2) as raw materials in an ammonia synthesis column. In this ammonia synthesis, when ammonia is separated from a synthetic gas in an ammonia synthesis loop, and a product ammonia is taken out as a liquid, a cooling process using a chiller refrigerant is used in general.
Conventionally, as a process using this refrigerant, for example, a part of the product ammonia extracted from the ammonia synthesis loop has been used as a chiller refrigerant, and has been used for cooling in the ammonia synthesis loop. The refrigerant (gas ammonia) after being used for cooling (after heat exchange) is compressed again, cooled, and liquified again to be circulated and used (Patent Literatures 1 and 2).